Non-volatile data storage devices, such as universal serial bus (USB) flash memory devices or removable storage cards, have allowed for increased portability of data and software applications. Flash memory devices can enhance data storage density by storing multiple bits in each flash memory cell. For example, Multi-Level Cell (MLC) flash memory devices provide increased storage density by storing 3 bits per cell, 4 bits per cell, or more. Although increasing the number of bits per cell and reducing device feature dimensions may increase a storage density of a memory device, a bit error rate of data stored at the memory device may also increase.
Error correction coding (ECC) is often used to correct errors that occur in data read from a memory device. Prior to storage, data may be encoded by an ECC encoder to generate redundant information (e.g. “parity bits”) that may be stored with the data as an ECC codeword. As more parity bits are used, an error correction capacity of the ECC increases and a number of bits required to store the encoded data also increases.
One source of errors that occur in data stored in a memory device is a result of read accesses to the memory device. When voltages are applied to a word line and to bit lines of a flash memory device to enable reading of stored data at the word line, threshold voltages of neighboring word lines may be disturbed (e.g., slightly increased) due to inter-cell coupling within the memory device. Read disturb effects are cumulative and, if not remedied, may result in a number of errors in stored data exceeding an ECC error correction capacity of a data storage device.